The present invention relates generally to medical stents (hereinafter xe2x80x9cstentsxe2x80x9d) and relates more particularly to stent delivery systems.
A stent is a tubular endoprosthesis placed within a body lumen to maintain its patency. For example, a stent may be used to maintain the patency of an esophagus or other passageway occluded by a tumor or of a blood vessel constricted by plaque. Most stents fall into one of the following two classes: (i) balloon-expandable stents; and (ii) self-expandable stents. Generally speaking, a stent delivery system includes the stent and some means for positioning and fixing the stent in place within a body lumen.
A balloon-expandable stent is typically a ductile metal tube. The delivery system for such a stent typically includes an inflatable balloon secured to the distal end of a catheter, the balloon-expandable stent being secured to the catheter over the inflatable balloon. In use, the catheter is introduced to a desired site within a body lumen, and the balloon is expanded until the stent positioned thereover is inelastically expanded to its desired size against the walls of the lumen. The balloon is then deflated, and the catheter is withdrawn from the site, thereby leaving the expanded stent in place against the walls of the lumen. An example of a balloon-expandable stent and delivery system therefor is disclosed in U.S. Pat. No. 4,922,905, inventor Strecker, issued May 1990, the disclosure of which is incorporated herein by reference.
A self-expandable stent is typically an elastic tube that self-expands after having been compacted. Illustrative examples of self-expandable stents are disclosed in the following documents, all of which are incorporated herein by reference: U.S. Pat. No. 5,876,445, inventors Andersen et al., issued Mar. 2, 1999; U.S. Pat. No. 5,366,504, inventors Andersen et al., issued Nov. 22, 1994; U.S. Pat. No. 5,234,457, inventor Andersen, issued Aug. 10, 1993; U.S. Pat. No. 5,061,275, inventors Wallsten et al., issued Oct. 29, 1991; Watkinson et al., xe2x80x9cThe Role of Self-Expanding Metallic Endoprostheses in Esophageal Strictures,xe2x80x9d Seminars in Interventional Radiology, 13(1): 17-26 (March 1996); and Strecker et al., xe2x80x9cNitinol Esophageal Stents: New Designs and Clinical Indications,xe2x80x9d Cadiovasc. Intervent. Radiol., 19:15-20 (1996).
The delivery system for a self-expandable stent typically comprises a catheter and a restraint for temporarily holding the stent in a compressed state at the distal end of the catheter. In use, the catheter is introduced to a desired site within a body lumen, and the restraint is removed, thereby allowing the stent to expand by its own elastic restoring force against the walls of the lumen. One of the more common self-expandable stent delivery systems of the above-described type comprises a coaxial tube assembly. More specifically, said delivery system comprises an inner catheter and an outer catheter, said outer catheter being coaxial with said inner catheter. The inner and outer catheters are appropriately sized so that a stent inserted over the distal end of the inner catheter is maintained in a compressed state by the inner surface of the outer catheter. In use, the assembly is introduced to a desired site, and the outer catheter is axially retracted relative to the inner catheter, thereby allowing the stent to self-expand off the inner catheter and against the walls of the lumen.
Illustrative examples of the aforementioned type of delivery system include the following U.S. patents, all of which are incorporated herein by reference: U.S. Pat. No. 5,484,444, inventors Braunschweiler et al., issued Jan. 16, 1996; U.S. Pat. No. 5,026,377, inventors Burton et al., issued Jun. 25, 1991; U.S. Pat. No. 4,990,151, inventor Wallstxc3xa9n, issued Feb. 5, 1991; and U.S. Pat. No. 4,732,152, inventors Wallstxc3xa9n et al., issued Mar. 22, 1988. A commercial embodiment of the above-described delivery system is the UNISTEP PLUS(trademark) delivery system (Boston Scientific Corporation, Natick, Mass.).
Although the above-described coaxial tube delivery system is well-suited for many types of self-expandable stents, such a delivery system is not particularly well-suited for those self-expandable stents that have limited axial strength, such as the Strecker stentxe2x80x94a knitted nitinol wire stent disclosed in U.S. Pat. No. 5,366,504 and commercially available from Boston Scientific Corporation, Natick, Mass. This is because such stents are often unable to resist becoming axially compressed during assembly of the coaxial tube delivery system, when the distal end of the outer catheter must be drawn across the stent, and/or during deployment of the coaxial tube delivery system, when the distal end of the outer catheter must be withdrawn across the stent.
Consequently, alternative delivery systems have been devised for use with the Strecker stent and with other like stents of limited axial strength. One such system, which is exemplified by the ULTRAFLEX(trademark) esophageal stent system (Boston Scientific Corporation, Natick, Mass.), comprises a stent of the aforementioned type, said stent being mounted on an inner catheter and being encased in a pharmaceutical grade dissolvable gelatin to maintain the stent in a compressed state. An outer catheter surrounds the gelatin-encased stent. In use, the system is inserted into a patient""s esophagus and the outer catheter is retracted. Moisture present in the esophagus causes the restraining gelatin to dissolve, thereby allowing the stent to expand.
Another delivery system devised for use with the Strecker stent and like stents of limited axial strength is disclosed in U.S. Pat. No. 5,405,378, inventor Strecker, which issued Apr. 11, 1995, and which is incorporated herein by reference. Said delivery system, which does not include an outer catheter, uses a crocheted suture cord to compress the stent against a catheter core. The crocheted cord is connected to a finger ring at the proximal end of the delivery system. Retraction of the finger ring unravels the cord in a circular manner down the length of the stent, gradually deploying the stent. A commercial embodiment of the aforementioned delivery system is the COVERED ULTRAFLEX(trademark) esophageal stent system (Boston Scientific Corporation, Natick, Mass.).
Unfortunately, the manufacture of the aforementioned crocheted cord delivery system is typically performed manually and can be quite taxing physically as a great deal of strength is required to tightly stretch the stent down on the catheter while crocheting the cord around the stent. Another problem with the foregoing system is that, during deployment, the crocheted cord does not always unravel correctly and completely.
It is an object of the present invention to provide a novel stent delivery system.
It is another object of the present invention to provide a stent delivery system as described above that overcomes at least some of the above-described shortcomings associated with existing stent delivery systems.
It is still another object of the present invention to provide a stent delivery system that has a minimal number of parts, that can be mass-produced, that is easy to manufacture and that is easy to use.
Therefore, in furtherance of the above and other objects to be described or to become apparent from the description below, there is provided herein a stent delivery system constructed according to the teachings of the present invention, said stent delivery system comprising, in one embodiment, (a) an inner catheter; (b) an outer catheter, said outer catheter surrounding at least a portion of the length of said inner catheter and adapted for axial movement relative to said inner catheter; (c) a self-expandable stent disposed between said inner catheter and said outer catheter; and (d) a stent restraining member disposed between said outer catheter and said self-expandable stent, said stent restraining member being dimensioned to maintain said self-expandable stent in a compressed state.
The aforementioned stent restraining member may be a braided tube (or any other type of tube) surrounding said self-expandable stent, said braided tube preferably being made from a strong, flexible, filamentary material having a low coefficient of friction. Examples of such materials may be a fine polyester or metal wire. The braided tube may be formed directly over the stent, preferably using an automated braiding machine, or may be pre-formed and then inserted over the stent. Where the braided tube is pre-formed and inserted over the stent, the system preferably further includes a braid holding sleeve secured to the inner catheter, said braid holding sleeve being adapted to receive the proximal end of the braided tube. The distal end of the stent restraining member is preferably mechanically coupled to the distal end of the outer catheter so that retraction of the outer catheter causes the stent restraining member to retract from the stent, thereby allowing the stent to self-expand.
Instead of being a tube, the stent restraining member may be a coil helically wrapped around the stent, said coil preferably being made from a strong, flexible, wire-like, thread-like or ribbon-like material having a low coefficient of friction.
The self-expandable stent is preferably a knitted mesh of nitinol wire flexible in both the radial and longitudinal axes, said stent preferably being coaxially positioned relative to the inner catheter and being stretched longitudinally thereacross.
The outer catheter may be a solid tube or may be a tube having a longitudinal split extending proximally from its distal end at least partially along its length. Where the outer catheter has a longitudinal split, said split is preferably sealed after the outer catheter has been advanced over and secured to the stent restraining member.
The stent delivery system preferably further comprises means for deterring said self-expandable stent from sliding proximally relative to said inner catheter during deployment, said deterring means further comprising a stent engaging sleeve fixed to said inner catheter, said self-expandable stent surrounding said stent engaging sleeve, said stent engaging sleeve having an outer surface adapted to engage said self-expandable stent in such a way as to deter said self-expandable stent from sliding proximally relative thereto.
In another embodiment, the stent delivery system of the present invention comprises (a) an inner catheter; (b) an outer catheter, said outer catheter surrounding at least a portion of the length of said inner catheter and adapted for axial movement relative to said inner catheter; and (c) a self-expandable stent disposed between said inner catheter and said outer catheter, said self-expandable stent being flexible in both the radial and longitudinal axes, said self-expandable stent being held in a compressed state by said outer catheter.
The aforementioned self-expandable stent is preferably a knitted mesh of nitinol wire coaxially mounted on said inner catheter. The outer catheter preferably has a longitudinal split extending proximally from its distal end at least partially along its length, said split preferably being sealed after the outer catheter has been advanced over and secured to the stent restraining member.
The stent delivery system preferably further comprises means for deterring said self-expandable stent from sliding proximally relative to said inner catheter during deployment, said deterring means further comprising a stent engaging sleeve fixed to said inner catheter, said self-expandable stent surrounding said stent engaging sleeve, said stent engaging sleeve having an outer surface adapted to engage said self-expandable stent in such a way as to deter said self-expandable stent from sliding proximally relative thereto.
The present invention is also directed to a method of manufacturing a stent delivery system, said method comprising, in one embodiment, the steps of (a) providing an inner catheter; (b) compressing a self-expandable stent over said inner catheter; (c) while said self-expandable stent is in a compressed state, positioning a braided tube around said inner catheter and said self-expandable stent, said braided tube being dimensioned to maintain said self-expandable stent in said compressed state; and (d) positioning an outer catheter around said braided tube, said outer catheter being adapted for axial movement relative to said inner catheter.
The aforementioned braided tube positioning step may comprise forming a braided tube over said self-expandable stent and said inner catheter or may comprise pre-forming a braided tube and then sliding said pre-formed braided tube over said stent and said inner catheter.
The stent and the inner catheter are preferably coaxially disposed, with said stent being flexible in both the longitudinal and radial axes. The aforementioned compressing step preferably comprises stretching said stent longitudinally across the length of said inner catheter.
Preferably, said method further comprises mechanically coupling said outer catheter to said braided tube for axial movement. The outer catheter may be a solid tube or may be a tube provided with a longitudinal slit extending at least a part of the length thereof. In the case of the tube with a longitudinal slit, the method preferably further comprises, after said outer catheter positioning step, the step of sealing said longitudinal slit.
The above method preferably further comprises, before said compressing step, the step of fixing a stent engaging sleeve to said inner catheter, said self-expandable stent surrounding said stent engaging sleeve, said stent engaging sleeve having an outer surface adapted to engage said self-expandable stent in such a way as to deter said self-expandable stent from sliding proximally relative thereto. In addition, said method preferably also comprises, before said outer catheter positioning step, the steps of fixing a braid holding sleeve to said inner catheter and securing the proximal end of said braided tube to said braid holding sleeve.
In another embodiment, the method of the present invention comprises the steps of (a) providing an inner catheter; (b) compressing a self-expandable stent over said inner catheter; (c) while said self-expandable stent is in a compressed state, wrapping a helical restraint around said inner catheter and said self-expandable stent, said helical restraint being dimensioned to maintain said self-expandable stent in said compressed state; and (d) positioning an outer catheter around said helical restraint, said outer catheter being adapted for axial movement relative to said inner catheter.
The aforementioned helical restraint is preferably made from a strong, flexible filamentary or ribbon-like material having a low coefficient of friction. Preferably, said method further comprises mechanically coupling said outer catheter to said braided tube for axial movement. The outer catheter is preferably a tube provided with a longitudinal slit extending at least a part of the length thereof, the method preferably further comprising, after said outer catheter positioning step, the step of sealing said longitudinal slit.
The subject method preferably still further comprises, before said compressing step, the step of fixing a stent engaging sleeve to said inner catheter, said self-expandable stent surrounding said stent engaging sleeve, said stent engaging sleeve having an outer surface adapted to engage said self-expandable stent in such a way as to deter said self-expandable stent from sliding proximally relative thereto.
In still another embodiment, the method of the present invention comprises the steps of (a) providing an inner catheter; (b) compressing a self-expandable stent over said inner catheter, said self-expandable stent being flexible in both the radial and longitudinal axes; and (c) positioning an outer catheter around said self-expandable stent, said outer catheter being adapted for axial movement relative to said inner catheter and being dimensioned to maintain said self-expandable stent in a compressed state.
Preferably, the aforementioned stent is a knitted mesh of nitinol wire. In addition, the outer catheter is preferably provided with a longitudinal slit extending at least a part of the length thereof, said method further comprising, after said outer catheter positioning step, the step of sealing said longitudinal slit.
The subject method preferably further comprises, before said compressing step, the step of fixing a stent engaging sleeve to said inner catheter, said self-expandable stent surrounding said stent engaging sleeve, said stent engaging sleeve having an outer surface adapted to engage said self-expandable stent in such away as to deter said self-expandable stent from sliding proximally relative thereto.
Additional objects, features, aspects and advantages of the present invention will be set forth, in part, in the description which follows and, in part, will be obvious from the description or may be learned by practice of the invention. In the description, reference is made to the accompanying drawings which form a part thereof and in which is shown by way of illustration specific embodiments for practicing the invention. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.